In the applications such as a filler for the semiconductor-encapsulation resin and a toner additive for electrophotography, fine silica particles having an average particle size of not larger than 1 μm have been widely used. This is because, when used as a filler for a semiconductor-encapsulation resin, the fine silica particles having the aforementioned particle size are advantageous for maintaining a homogeneous composition since they precipitate little when the resin compound is in a molten state or in a liquid state (also referred to as liquid resin). Furthermore when used as a toner additive for electrophotography, the fine silica particles having the above particle size adhere to the toner surfaces and are advantageous for improvement of free-flow properties.
There have heretofore been made many reports about the use of fumed silica (so-called dry silica) particles produced by a flame hydrolysis process of chlorosilane as a filler for the semiconductor-encapsulation resin (see, for example, a prior document A).
Prior document A: JP-A-1-161065
In recent years, the enhanced sensitivity to environmental problems has grew a trend to use lead-free solders to mount semiconductor packages on circuit boards. The use of lead-free solders, however, causes an increase in temperature at which the packages are mounted and requires improvement of heat resistance of the packages. That has led to the higher filler content of the semiconductor resin compound.
Even at low content of the liquid resin, however, the aforesaid fumed silica substantially enhances of viscosity. At high content of the resin, therefore, it is difficult to mold the semiconductor-encapsulation resin.
To suppress the enhancement viscosity by adding the fumed silica particles to the resin at high content the use of a spherical fused silica having an average particle size which is controlled to be not larger than 1 μm has been proposed. (see, for example, a prior document B).
Prior document B: JP-A-8-245214
Indeed, the use of the spherical fused silica prevents enhancement of the viscosity of the resin and the silica can be filled at high content of the resin, but the resin compound comprising the spherical fused particles doesn't have satisfactory strength.
There have further been reports about the use of the fumed silica as a toner additive for electrophotography (see, for example, a prior document C). Due to its complex particle structure, however, the fumed silica doesn't improve free-flow properties of the toner. There has further been some reports about the use of the spherical fused silica as a toner additive (see, for example, a prior document D). Due to its spherical shape, however, the spherical fused silica particles don't significantly toner surfaces; i.e., the toner particle surfaces from which the fine silica particles are removed come in contact with the photoconductor surface. That causes a problem in that the toner particles is not transferred onto the paper and remain on the photoconductor surfaces.
Prior document C: JP-A-2002-116575
Prior document D: JP-A-2002-154820